I do my art in blocks: photography, then developing, then treatments and painting, then uploads. Sometimes I have such fun with the creating process that I end up with a rather large backlog to upload. I recently uploaded 30 images. Usually, however, I do anywhere from 1 to 5 at a time as they become ready. I would never purposefully delay uploading.
As Mike said, advertising them all at once can look like spam, so when I upload a bunch at once, I create a slide show with a single link that shows "new work available for your enjoyment." That is far better than sending out notices on each piece. Later, I can send out individual notices, well-spaced in time, to promote pieces I really want seen.